In medical education, even well-intentioned learners struggle to change their practice. This intention-action gap is a well-described phenomenon. Strong commitment to changing behaviors is important, but by itself it is only a modest predictor of goal attainment.Implementation intentions are an extensively studied strategy from cognitive psychology that have been shown to close the intention-action gap and increase goal attainment across myriad domains. Implementation intentions are "if-then" plans that specify an anticipated future situation and a planned response-"If I encounter situation X, then I will respond with action Y." They differ from simple goals, which specify only a desired behavior or outcome-"I intend to perform action Z." Despite this subtle difference, they have shown substantial effectiveness over goals alone in increasing goal attainment.In this article, the authors first describe implementation intentions, review the substantial body of evidence demonstrating their effectiveness, and explain the underlying psychological mechanisms. They then illustrate the connections between implementation intentions and established learning theory. The final section focuses on forming effective implementation intentions in medical education. The authors provide concrete examples across the continuum of learners (from medical students to attending physicians) and competencies, and make recommendations for when and how to employ implementation intentions.